Rotary injectors were used to treat molten aluminum, such as disclosed in U.S. Pat. No. 6,960,239 for instance. In these applications, a rotary injector, known as a rotary flux injector, was used to introduce particulate material into molten aluminum held in a large volume furnace.
An example of a known rotary flux injector is shown in FIG. 1 as having a rotary shaft 15, typically made of a temperature resistant material such as graphite, leading to an impeller 16 mounted to the end thereof. A supply conduit is provided along the shaft and leads to an axial outlet across the impeller 16. A fluxing agent, typically in the form of a mixture of particulate salts, is entrained along the supply conduit by a carrier gas. The impeller 16 has blades or the like to favour the integration of the fluxing agent in the molten metal, in an action referred to as shearing. The geometrical design of the impeller was directly related to shearing efficiency, and radially-oriented blades generating a radial thrust inside the molten metal were used to this end. The depth d at which the impeller 16 is rotated in the molten metal corresponds to the distance between the upper edge of the impeller 16 and the melt surface 13. Traditionally, a minimal depth d was prescribed for the impeller to correctly operate. The minimal depth d was equal to or above the diameter of the impeller, depending on the applications.
It is also common to introduce alloy ingredients into the molten aluminum. Once the alloy ingredients were introduced, a boat propeller like impeller with slanted blades was rotated inside the molten metal for mixing the alloy ingredients evenly in the molten aluminum. Impellers with slanted blades produced an axial thrust inside the molten metal, and axial thrust was associated to mixing efficiency.
All these steps correspond to a significant amount of time required to produce a batch of aluminum in a furnace; and it can thus be understood that although known rotary flux injectors and rotary mixers were satisfactory to a certain degree, the overall process duration limited the overall productivity of aluminum production plants. There was thus a general need to gain further efficiency.